This blog began through a NIFA grant for Missouri Beginning Farmers. It continues today as a way for beginning farmers to learn about new ideas and to hear about upcoming events of interest. It is maintained by Debi Kelly (kellyd@missouri.edu).

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As an Extension Associate with the University of Missouri, I work with beginning farmers, small farms, alternative agriculture and organic farming. I am also the Co-coordinator for the Missouri Sustainable Agriculture and Research (SARE) Education Professional Development Program (PDP).

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Monday, July 14, 2014

Herbicide Carryover in Garden Mulch and Manure

During the summer, MU Extension offices get phone calls from homeowners as well as farmers asking what is wrong with their vegetables. Not always but at times, vegetables show herbicide damage even on vegetables that have not had any sprayed herbicide nearby.

Herbicide carryover has become an increasing
problem in gardens and greenhouses. Depending on the active ingredient in the
herbicide and weather conditions, herbicide effects can linger in the soil for
years.

“These are the same
signs one would see in a case of spray drift from herbicides, however if there
is no possibility of spray drift, herbicide carryover in mulches and manure
compost introduced from another location should be considered,” said Jill
Scheidt, agronomy specialist with University of Missouri Extension.

According to Tim
Baker, horticulture specialist with University of Missouri Extension in Daviess
County, there are two instances where he has observed irregular herbicide
carryover in mulches and manure compost.

The first situation
is that of herbicides surviving the intestinal tract of an animal, in a high
enough concentration to cause crop damage. In this case, a broadleaf
herbicide is sprayed on a pasture, creating lush grasses for the animal to feed
on. When the manure is collected, the herbicide is still there. The
second situation is the possibility of herbicide being applied to a field, and
then manure collected for composting.

In order for most
chemicals to speed the process of breaking down, sunlight, air and water must
be in the equation. Wet, warm weather promotes the process of chemical
breakdown. If there is contamination in a covered greenhouse, consider opening
the greenhouse to the outside elements.

If that is not an
option, Baker suggests using activated charcoal to absorb the herbicide. In
some instances, herbicide can take a number of years to leave the soil, plants
may improve, but slight signs of injury can still be seen.